The recent encouraged global activities of environmental protection put strong-demands for restrictions on greenhouse gases and NOx gas production. In order to reduce the total amount of such exhaust gases, practical application of fuel cell system to automobile is thought to be very useful.
Polymer electrolyte fuel cells (PEFCs) have several advantages: operative at a low temperature; high power density; and generation of water alone during power generating reaction. Among all, PEFCs using methanol as fuel are thought to be a promising power source for an electric automobile since they enables fuel supply in a liquid form like gasoline.
PEFCs are classified into two types: reformed methanol-type polymer electrolyte fuel cells which involve reforming methanol into hydrogen-containing gas using a reformer; and direct methanol polymer fuel cells (DMFCs) which utilize methanol directly without using a reformer. Practical use of direct methanol polymer fuel cells is expected due to their great advantages: 1) weight-saving is possible since direct methanol polymer fuel cells do not require a reformer; 2) resistance against frequent start and stop operations; 3) significantly improved load change response; and 4) substantially reduced catalyst poisoning.
However, although as the electrolytic substance for PEFC using methanol fuel, the electrolyte membrane is required to have the following; i) the inhibition of permeation of methanol (the electrolytic substance is impermeable to methanol); ii) durability, more particularly, heat resistance for operation a high temperature (80° C. or higher); iii) no or reduced change in surface area following the wetting with a solution and drying at starting and stopping; iv) proton conductivity; v) thin film formability; and vi) chemical durability, any electrolyte membrane which could sufficiently satisfy these requirements has not been made available yet.
Further, in from a viewpoint of a portable type methanol fuel PEFC, i) the inhibition of permeation of methanol is important and operation-ability near a normal temperature is important, while the durability at a high temperature becomes less important.